1. Field of the Invention
The present invention relates to a hydraulic shock absorber which may be suitably used not only to support, for example, the body of a vehicle on an axle thereof, but also to adjust the level at which the body of the vehicle is disposed from the ground. More particularly, the present invention pertains to a hydraulic shock absorber which includes a detector for detecting the amount by which the piston rod projects from the shock absorber body;
2. Description of the Prior Art
FIG. 1 shows a prior art hydraulic shock absorber.
In the figure reference numeral 1 denotes a body of a hydraulic shock absorber 50. A bracket 2 is rigidly secured to the lower end of the shock absorber body 1 for the purpose of mounting the shock absorber body 1 to an axle (not shown) of a vehicle. The bracket 2 is provided with mounting bores 2A for receiving bolts or the like. References numeral 3 denotes a piston rod which projects axially from the upper end of the shock absorber body 1. The diameter of the projecting end portion of the piston rod 3 is stepped in two stages to define a shoulder portion 3A and a small-diameter portion 3B. An inner bore 3C for supplying and discharging compressed air is provided in the projecting end portion of the piston rod 3, the bore 3C consisting of a first portion which extends axially from the upper end face of the small-diameter portion 3B and a second portion which extends radially. The piston rod 3 reciprocates relative to the shock absorber body 1 in response to vibrations of the vehicle when running so as to operate a piston received in the shock absorber body 1 to generate a damping force.
The reference numeral 4 denotes a shell which is rigidly secured at its proximal end 4A to the shoulder portion 3A of the piston rod 3 by means of a nut (not shown) so that the shell 4 is displaced together with the piston rod 3 in one unit. The shell 4 has the shape of a tube having its proximal end 4A closed so that the shell 4 surrounds the projecting end portion of the piston rod 3. The diameter of the shell 4 is smaller at its distal end portion than at its proximal end to thereby define a reduced-diameter portion 4B. Reference numeral 5 denotes a tubular member which is rigidly secured at its proximal end 5A to the outer periphery of the intermediate portion of the shock absorber body 1 by welding or other similar means. The tubular member 5 consists of a bottom portion 5B which extends radially outward from the proximal end 5A and a tubular portion 5C which extends axially upward from the outer peripheral edge of the bottom portion 5B to a location disposed above the upper end of the shock absorber body 1 so that the tubular portion 5C surrounds the body 1. Thus, the tubular member 5 is integral with the shock absorber body 1. The shell 4 and the tubular member 5 are eccentric with respect to both the shock absorber body 1 and the piston rod 3 in order to accommodate a sensor 12 (described later) in the space defined between the shell 4 and the tubular member 5.
Reference numeral 6 denotes a rubber member which cooperates with the shell 4 and the tubular member 5 to define an air chamber 7 therein. The rubber member 6 is bent at its intermediate portion 6A so as to have a substantially U-shaped cross section. The outer peripheral edge 6B is hermetically secured to the reduced-diameter portion 4B of the shell 4 by means of a ring 8, while the inner peripheral edge 6C is hermetically secured to the distal end of the tubular portion 5C of the tubular member 5 by means of a ring 9. The rubber member 6 is elastically deformable, thereby enabling the shell 4 and the tubular member 5 to move toward and away from each other in response to the retraction and extension of the piston rod 3. Reference numeral 10 denotes a rubber stopper which is disposed around the projecting end portion of the piston rod 3, and 11 a passage which is provided at the upper end of the rubber stopper 10 and extends radially. The passage communicates with the inner bore 3C to supply and discharge compressed air to and from the air chamber 7 through the inner bore 3C. Thus, the air chamber 7 is expanded or contracted under the action of compressed air supplied to or discharged from the air chamber 7 through the passage 11 to cause the shell 4 to move upward or downward in accordance with the level of pressure inside the air chamber 7, thereby controlling the amount by which the piston rod 3 projects from the shock absorber body 1, and thus appropriately adjusting the level at which the vehicle body is disposed with respect to the ground.
The reference numeral 12 denotes a sensor which is disposed inside the air chamber 7 to detect the level of the vehicle in accordance with the degree of expansion or contraction of the air chamber 7. The sensor 12 comprises a rod 13 which is hermetically secured at one end 13A thereof to the proximal end 4A of the shell 4 and which extends axially downward inside the air chamber 7 with the other end 13B being a free end, and a plurality of (e.g., three) reed switches 14A, 14B, 14C serving as sensor elements which are disposed at predetermined intervals inside the rod 13 between the ends 13A and 13B. Each of the reed switches 14A, 14B, 14C is activated when approaching a magnet 17 (described later) so as to output, through a lead wire 15, a signal representative of the level of the vehicle that is, a signal used to detect whether the body of the vehicle is disposed at a high position, an intermediate position or a low position with respect to the ground. The rod 13 extends axially inside the air chamber 7 so that, even when the body of the vehicle is at the high position as exemplarily shown in the figure, the lower end 13B is below the magnet 17 which is provided at the upper end of the shock absorber body 1.
Reference numeral 16 denotes an L-shaped supporting bracket which is provided at the upper end of the shock absorber body 1, and the magnet 17 serves as an object to be detected which is secured to the upper side of the supporting bracket 16. The magnet 17 is disposed at substantially the same level as the upper end of the shock absorber body 1 so that the magnet 17 is in close proximity with the rod 13. The magnet 17 is adapted such that, when a reed switch 14A, 14B or 14C approaches it in response to the contraction or expansion of the air chamber 7, the magnet 17 causes the contacts of the reed switch to close so as to output a signal representative of the detected level of the vehicle. The magnet 17 is disposed at a location in which there is no possibility that the magnet 17 will come into contact with the rubber stopper 10 or the proximal end 4A of the shell 4 when the piston rod 3 is retracted. In addition, reference numeral 18 denotes a rubber stopper receiver which is rigidly secured to the upper end of shock absorber body 1 by welding or other similar means to contact the rubber stopper 10.
In the hydraulic shock absorber arranged as described above, the bracket 2 is secured to an axle of a vehicle, while the small-diameter portion 3B of the piston rod 3 is secured to the body of the vehicle, thereby supporting the body and also enabling the level of the body of the vehicle to be appropriately adjusted by supplying or discharging compressed air to or from the air chamber 7, as described above. More specifically, dry compressed air is supplied from a compressed air tank (not shown) into the air chamber 7 or discharged therefrom through the inner bore 3C and the passage 11 to expand or contract the air chamber 7, thereby controlling the amount by which the piston rod 3 projects from the shock absorber body 1, and thus appropriately adjusting the level of the vehicle.
When the vehicle is at the high position as illustrated, the reed switch 14 A is closet to the magnet 17, and therefore the reed switch 14A is activated to output a signal representative of the fact that the vehicle is at the high position. When the compressed air inside the air chamber 7 is discharged through the passage 11 and the inner bore 3C to thereby contract the air chamber 7, the piston rod 3 is retracted. Accordingly, the rod 13 of the sensor 12 moves axially downward, and the reed switch 14B confronts the magnet 17. Therefore, the reed switch 14B is activated to output a signal representative of the fact that the vehicle is at the intermediate position. When the reed switch 14C confronts the magnet 17, it is activated to output a signal representative of the fact that the vehicle is at the low position.
The above-described prior art shock absorber suffers, however, from the following problems. The rod 13 of the sensor 12 which constitutes the level detector extends axially inside the air chamber 7 and the rod 3 is supported only at one end 13A thereof in a cantilever fashion by the proximal end portion 4A of the shell 4. Accordingly, if the shell 4 oscillates sideward when the piston rod 3 is extended or retracted, the lower end 13B of the rod 13 oscillates sideward to a substantial extent. In such a case, when the reed switch 14A, 14B or 14C confronts the magnet 17, the predetermined distance between the reed switch and the magnet 17 changes. Therefore, an erroneous detection is likely to occur. Furthermore, a bore for facilitating the mounting of the end 13A of the rod 13 must be provided in the proximal end portion 4A of the shell 4, and the presence of this mounting bore an contribute to the disadvantage of compressed air in the air chamber 7 leaking out through the area between the outer periphery of the rod 13 and the peripheral edge defining the bore, and it is therefore difficult to ensure airtightness.